Oh, these two guys were in it as well...James Darren and Robert Colbert.
The unfortunate pattern with this series, as with so many others in the genre was the disintegration of the story quality. This was a repeating failure with Irwin Allen productions and stands as proof that its the story that matters most; all the special effects in the world can't save a yarn which breaks the suspension of disbelief by disrespecting its own conventions. The Irwin Allen series tended to veer into the realm of the fantastic rather than the far-fetched. What's the difference? The far-fetched may be excused as a necessary convention of the theatre. In this category are the English-speaking French, Mongols, Renaissance Venetians, Russians, aliens etc. whom the boys encounter. It's obviously baloney but a remotely realistic treatment would have each episode consumed with communicative antics and a dialogue consisting mostly of "I can't understand you" and less polite versions in multiple tongues. Thus also for the artificial gravity in space craft. Artificial gravity is anomalous to the spacecraft design because it's a technology usually way beyond everything else aboard...just like the Star Trek transporter.
Where the fantastic and bizarre intrude is with the introduction of entities such as the ghost of the Emperor Nero, Merlin the Wizard and utterly crazy storylines such as the one where the aliens turn up in the bunker and want to know what happened to their raiding party which visited Earth during the 19th Century. These critters are from a culture which has practiced and recently abandoned piracy as an economic model. They want to be assured that the humans didn't zap their boys...otherwise they'll destroy Earth. They're eventually placated by seeing their colleagues' ship leaving Earth intact through the Time Tunnel video scanner. Then they leave. So how do they know the temponauts were near their pals anyway? If they can figure that, why do they need the humans to tell them what happened? Aren't they remotely impressed by the fact that Earth has time travel? Don't they want to buy it/steal it?
The Tunnel remains a tantalising conceit for all that. Now if only someone would do a quality remake...